Image forming systems which exhibit ultra-high contrast (especially those with a gamma of 10 or above) are essential for achieving good reproduction of continuous tone images by means of a screened image and good reproduction of line images in the graphic arts field.
U.S. Pat. Nos. 4,224,401, 4,168,977, 4,166,742, 4,311,781, 4,272,606 and 4,211,857, etc. disclose methods in which high contrast photographic characteristics are obtained using stable development baths in which use is made of hydrazine derivatives. Photographic characteristics with high speed at ultra-high contrast are obtained with these methods, and moreover the presence of high concentration of sulfite can be tolerated in the development bath, and so the stability of the development bath in response to aerial oxidation is much better than that of the lith developers.
However, the hydrazine compounds known in the past have had a number of distinct disadvantages. Thus attempts have been made to provide hydrazine compounds with structures which are fast-to-diffusion. Such attempts have been made with a view to reducing the level of the adverse effects on other photographic materials caused by the washing out of the conventional hydrazine compounds into the development processing bath. These non-diffusible hydrazine compounds must be used in large quantities in order to provide sensitization for contrast enhancement, and the large quantities occasionally lead to a deterioration of the physical strength of the photosensitive layers obtained. The large quantities also cause problems with the precipitation of the hydrazine compounds in coating liquids. Moreover, it has not been possible to obtain a sufficiently high contrast when processing has been carried out in an exhausted development bath in which a large quantity of photosensitive material has been processed.
The provision of very high contrast images using hydrazines which have a substituent group which is readily adsorbed on silver halide grains has been disclosed in U.S. Pat. Nos. 4,385,108, 4,269,929 and 4,243,739. However, although contrast is enhanced with these adsorption type hydrazine compounds, the maximum image density obtained is low, and there is also a problem with printing materials. The problems is that reduction, as routinely performed, is virtually impossible since the image density is inevitably low before reducing the screen area. Moreover, if the material is processed in an exhausted bath which has undergone aerial oxidation, then there are problems with large fluctuations on the high speed side.
The contrast enhancing ability of the conventional hydrazine compounds is inadequate, as has been indicated above. Therefore, the compounds must be used in large quantities, and this may have an adverse effect on the physical properties of the film. The maximum image density may become inadequate and problems can arise with large fluctuations in the photographic characteristics depending on the working state of the development bath. The resolution of these problems is clearly desirable.